Pretty on the Inside

There is a revolution afoot in microscopy, as biophysicists come up with ways to image the nanoscale structures of living cells. Using a new technique called 3-D structured-illumination microscopy, researchers at the University of California, San Francisco, have made some of the most detailed optical images yet of the interior workings of cells, and they are gorgeous.

The resolution of conventional microscopes is limited by the size of the spot of light used to scan a surface. For more than a hundred years, biophysicists have run up against a fundamental limit: using lenses, it’s not possible to focus light down to a spot size smaller than half its wavelength. So the inner workings of living cells have been impossible to resolve. Biologists have sequenced the genome, but it’s still something of a mystery how DNA, RNA, proteins, and other molecules interact in live cells. These parts are visible using electron microscopy, but this process can only be employed on dead cells. Images of live cells taken with conventional light microscopes reveal only a blur. Understanding the inner workings of cells could shed light on disease.

“We threw the conventional microscope out the window and began again,” says John Sedat, a professor of biochemistry and biophysics at the University of California, San Francisco. Instead of focusing a small spot of light onto cells, the new microscope, which has a resolution of about 100 nanometers, illuminates cells with stripes of light called an interference pattern. When a fine cellular structure, such as a single cluster of proteins embedded in a cell nucleus, reflects this light, it changes the pattern slightly. The microscope collects this light; software is used to interpret changes in its pattern and create an image.

Sedat and his group played a major role in developing this technique, initially for two-dimensional imaging. Their new work, described this week in the journal Science, involved creating 3-D images of the nucleus, the structure that holds the lion’s share of the genome. The next step, says Sedat, is to decrease the amount of cell-damaging light needed to make the pictures to ensure that the cells remain healthy during the imaging process.

Click here to launch a slide show of images that reveal the cell at an unprecedented level of detail.